#!/usr/bin/env bash
set -Eeuo pipefail
shopt -s inherit_errexit nullglob

# -----------------------------------------------------------------------------
# CONFIGURATION
# -----------------------------------------------------------------------------
readonly BACKUP_BASE=/media/extension/backup/ubuntu
readonly MOUNT_POINT=/media/extension
readonly NOW=$(date +'%Y-%m-%d')
readonly THIS_RUN="${BACKUP_BASE}/${NOW}"
readonly LATEST="${BACKUP_BASE}/latest"

# Directories (or files) to back up (without DB volumes)
declare -a SOURCE_ITEMS=(
  "/home/oster/server"
#  "/home/oster/photo-lib"
)

# Rsync exclusions — exclude DB-related dirs that are dumped separately + common junk
declare -a EXCLUDES=(
  --exclude='.cache'
  --exclude='node_modules'
  --exclude='*.tmp'
  --exclude='**/postgresql'
  --exclude='**/mysql'
  --exclude='**/db'
  --exclude='**/database'
)

# Rsync options
RSYNC_OPTS=(
  -aAXHv                # preserve everything, human-friendly, verbose
  --delete              # mirror deletions
  --partial             # keep partials if interrupted
  --stats               # summary
  "${EXCLUDES[@]}"
)

# -----------------------------------------------------------------------------
# LOGGING
# -----------------------------------------------------------------------------
log() { echo "[$(date +'%F %T')] $*"; }
die() { log "FATAL: $*"; exit 1; }

# Locking
lockfile="${BACKUP_BASE}/.backup.lock"
cleanup() { rm -f "$lockfile"; }
trap cleanup EXIT
if ! ( set -o noclobber; echo "$$" > "$lockfile" ) 2>/dev/null; then
  die "Another backup is already running (lockfile exists at $lockfile)."
fi

# -----------------------------------------------------------------------------
# FUNCTIONS
# -----------------------------------------------------------------------------
check_mount() {
  if ! mountpoint -q "$MOUNT_POINT"; then
    die "Backup mountpoint $MOUNT_POINT is NOT mounted."
  fi
}

# Rotation: keep 7 daily and 4 weekly
rotate_old() {
  log "Applying retention policy (7 daily, 4 weekly)."
  cd "$BACKUP_BASE" || die "Cannot cd into $BACKUP_BASE"

  # find snapshot dirs YYYY-MM-DD only
  for dir in $(ls -1 | grep -E '^[0-9]{4}-[0-9]{2}-[0-9]{2}$'); do
    keep=0

    # Keep last 7 daily
    for i in $(seq 0 6); do
      [ "$dir" = "$(date -d "-$i day" +%F)" ] && keep=1
    done

    # Keep last 4 Sundays (weeklies)
    for i in $(seq 0 27); do
      d=$(date -d "last sunday -$i week" +%F)
      [ "$dir" = "$d" ] && keep=1
    done

    if [ $keep -eq 0 ]; then
      log "  Deleting expired snapshot $dir"
      rm -rf "$dir"
    else
      log "  Keeping snapshot $dir"
    fi
  done
}

# -----------------------------------------------------------------------------
# MAIN
# -----------------------------------------------------------------------------
log "=== Starting backup run: $NOW ==="
check_mount

mkdir -p "$BACKUP_BASE" "$THIS_RUN"

# Incremental snapshot?
if [ -d "$LATEST" ]; then
  LINK_DEST="--link-dest=$(readlink -f "$LATEST")"
  log "Using link-dest for incremental snapshot → $LATEST"
else
  LINK_DEST=""
  log "No previous backup; creating full snapshot."
fi

# Run backups
for src in "${SOURCE_ITEMS[@]}"; do
  base=$(basename "$src")
  dst="${THIS_RUN}/${base}"
  mkdir -p "$dst"
  log "Backing up $src → $dst"
  nice -n 10 ionice -c2 -n7 \
    rsync "${RSYNC_OPTS[@]}" $LINK_DEST \
      "$src"/ "$dst"/
done

# Update latest symlink atomically
ln -sfn "$(basename "$THIS_RUN")" "$BACKUP_BASE/.latest.tmp"
mv -T "$BACKUP_BASE/.latest.tmp" "$LATEST"

log "Snapshots done. Running rotation policy..."
rotate_old

log "=== Backup completed successfully ==="